The bandwidth of a television signal is a function of the spatial (horizontal, vertical) and temporal resolution to be contained therein. As increased resolution is desired in either the vertical, horizontal or temporal directions the bandwidth of the signal must be increased. HDTV signals contain considerably more resolution than, for example, standard NTSC encoded signals. As a result various ways have been proposed to generate and transmit HDTV signals, some of which are compatible to a greater or lesser degree with NTSC receivers and some which are designed to replace the NTSC standard altogether.
In order for an HDTV system to gain wide acceptance, however, the economic reality of a $100 billion investment (in North America alone) in NTSC television receivers, must not be ignored. At the same time the trade off for compatibility must not stifle the potential of a true HDTV system.